Ion mobility spectrometry (IMS) is a technique for separating and identifying ions. IMS can be employed to separate structural isomers and resolve conformational features of macromolecules. IMS may also be employed to augment mass spectroscopy (MS) in a broad range of applications, including metabolomics, glycomics, and proteomics.
For example, when performing IMS, a sample containing different ions is injected into a first end of an enclosed cell containing a carrier gas, also referred to as a buffer gas. In the cell, the ions move from the first end of the cell to a second end of the cell under the influence of an applied electric field. The ions are subsequently detected at the second end of the cell as a current as a function of time. The sample ions achieve a maximum, constant velocity (i.e., a terminal velocity) arising from the net effects of acceleration due to the applied electric field and deceleration due to collisions with the buffer gas molecules. The terminal velocity of ion within the IMS cell is proportional to their respective mobilies, related to ion characteristics such as mass, size, shape, and charge. Ions that differ in one or more of these characteristics will exhibit different mobilities when moving through a given buffer gas under a given electric field and, therefore, different terminal velocities. As a result, each ion exhibits a characteristic time for travel from the first end of the cell to the second end of the cell. By measuring this characteristic travel time for ions within a sample, the ions may be identified.
There are a number of IMS formats used for chemical and biochemical analysis, including constant field drift tube ion mobility spectrometry (DT-IMS), high field asymmetric ion mobility spectrometry (FA-IMS), differential mobility analysis (DMA), and traveling wave ion mobility spectrometry (TW-IMS). These formats vary in the manner by which the electric field is applied to separate the ions within the IMS cell. Notably, however, conventional IMS devices are limited in their ability to separate ions (separation power) due to practical limitations on size and complexity of the electrode structures generating the electric fields that separate the ions.
Accordingly, there exists an ongoing need for improved systems and methods for ion mobility separation.